FIG. 6 illustrates the configuration of a conventional laser processing apparatus. In FIG. 6, the laser processing apparatus drills a fine hole in a workpiece such as substrate 57 by irradiating the workpiece with a laser beam. A description is made for the configuration of the conventional laser processing apparatus.
First, laser beam 52 is emitted from laser oscillator 51, direction-converted by reflecting mirror 53a, and then is led from reflecting mirror 53b, 53c toward galvanometers 54, 55 including a two-axis (X, Y) galvanometer mirror. Then, laser beam 52 is launched into fθ lens 56 with its irradiation direction changed by the operation of galvanometers 54, 55 and focused, then substrate 57 positioned on XY table 58 is irradiated with laser beam 52.
Substrate 57 is irradiated with laser beam 52 while scanning processed area A, a given range of substrate 57, in the direction X-Y. At the time when irradiating processed area A completes, XY table 58 is moved in direction X, Y, or X and Y, and after the next processed area is reached, substrate 57 is laser-processed again.
In the same way, areas of substrate 57 to be processed are sequentially processed.
For example, patent literatures 1 and 2 are known as information on prior art documents related to the present invention.
Here, when processing a through hole by a laser processing method using the above-described laser processing apparatus, a space is required between XY table 58 and substrate 57. Meanwhile, for a non-through hole, no space is required.
Conventionally, a through hole is processed with such a jig placed on the XY table; a non-through hole is processed with the substrate placed on the XY table.
More specifically, when forming a through hole in a thin sheet made of a material referred to as prepreg that is woven or nonwoven fabric impregnated with resin and partially hardened (prepreg sheet hereinafter), or in a thin sheet provided with copper foil (including a conductor circuit) on its outer layer, processing is made with a jig for pulling the ends of the sheet to retain the thin sheet in midair while tensioning it.
Particularly, when providing a through hole in a prepreg sheet, if performing laser processing after positioning the prepreg sheet directly on the XY table and placing it on the table, the resin partially hardening in the prepreg sheet is deposited on the XY table due to heat during the laser processing, preventing a desired through hole from being formed, and thus requiring the above-described jig for pulling the ends of the sheet.
However, if retaining the prepreg sheet in midair while tensioning it with a jig for pulling the ends of the sheet, a thin prepreg sheet with the resin partially hardening may undesirably change in its processing dimensions during laser processing. Especially for a multilayer printed wiring board in which a prepreg sheet with a conductive paste filling a hole to be processed by laser used as an interlayer connector, deviation in the position of an interlayer conducting hole occurs due to a dimensional change and unevenness of the prepreg sheet, possibly decreasing the reliability in electrical connection.
Meanwhile, in a process of manufacturing what is called a build-up multilayer printed wiring board provided with a non-through conducting hole in its outer layer, to form a non-through hole in the outer layer, processing needs to be made by positioning a sheet-like substrate on the XY table and placing the substrate on the table, and by sucking the substrate at its bottom surface to fix it. The reason is, if the sheet-like substrate of the build-up multilayer printed wiring board, usually having a multilayered structure of 4 to 10 layers, is retained in midair using a jig for pulling the ends of the sheet, deformation caused by the own weight occurs, thereby preventing a non-through hole in the outer layer to be formed with a high degree of accuracy.
Accordingly, handling has been made to form both non-through and through holes in a sheet-like substrate as the following. That is, laser processing is made while the sheet is retained in midair using a jig for pulling the ends of the sheet for a through hole; the sheet is placed on the XY table for a non-through hole.
However, the above-described conventional method results in executing setting of the laser processing apparatus twice for hole drilling in one sheet-like substrate, which may lower the accuracy in the position of holes, significantly decreasing the productivity for printed wiring boards.
[Patent literature 1] Japanese Patent Unexamined Publication No. H11-254166
[Patent literature 2] Japanese Patent Unexamined Publication No. 2000-233291